Absence of binding of MDP, a synthetic immunoadjuvant, to anti-peptidoglycan antibodies.

The binding of the synthetic immunoadjuvant N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP, for muramyl dipeptide) to human and rabbit sera containing peptidoglycan (PG) antibodies was investigated. Studies were performed by employing the corresponding 14C or 125I-labeled compounds in Farr-type binding and inhibition assays. Whereas MDP did not react with naturally occurring or experimentally induced PG-antibodies, the analog of MDP MDP-L-Lys-D-Ala did bind to hyperimmune rabbit anti-PG sera, but not to the human sera tested. These studies indicate that the radioimmunoassays employed basically are applicable for the selection of nonimmumogenic MDP analogs possessing immunoadjuvant activity.